Electrical apparatus



O R Y 8 w 6 Ema 0 a a o 2, Wk 5 m c A a a h S r L F m Am ww F m AA PI E E mm m m w E E E m m May 29, 1951 Original Filed April 7, 1945 RESISTANCE I I I I Ma 29,1951 1 F. P, VAC 'A 2,555,208

ELECTRICAL APPARATUS Original Filed April '7, 1945 2 Sheets-Shee-i 2 H-nuuums RANGE INVENTOR o nod 75 B000 SPEED r Vac/1w.

ATTORNEY Patented May 29, 1951 ELECTRICAL APPARATUS Fred P. Vacha, Auburndale, Mass., asslgnor, by mesne assignments, to National Pneumatic 00., Inc., Boston, Mass, a corporation of Delaware Original application April 7, 1945, Serial No.

587,103. Divided and this application September 3, 1948, Serial No. 47,657

5 Claims.

The present invention relates to electrical apparatus and more particularly to electrical resistance apparatus of the type employing a plurality of compressible elements whose resistance characteristics vary in accordance with pressure applied thereto.

An object of the invention is to provide a resistance assembly of the pressure responsive type, such as a carbon pile resistor, supported and acted upon in such manner as to be shiftable as a unit toward and away from end reaction abutments, whereby there isprovided a freely floating assembly more readily capable of adjusting itself under all conditions so that the pressure application always tends to be along true parallel lines with respect to all individual components of the stacked assembly or pile.

In the accompanying drawings illustrating one application of the invention and in the following description of said application of the invention, the novel resistance apparatus is shown in association with speed responsive mechanism including a centrifugal governor and springs for applying pressure to the resistance assembly; this being the particular application of the invention which is described and claimed in my parent application No. 587,103 filed April 7, 1945, now Patent No. 2,460,246, issued January 25, 1949.

It is to be understood, however, that the novel resistance mechanism herein claimed per se is capable of use in other associations, as will be apparent to those skilled in the art upon examination of the following disclosure and are to be considered as embraced in the appended claims.

In the accompanying drawings, Fig. 1115a sectional plan view of the preferred governor; Fig. 2 is an end elevation of the stationary unit; Fig. 3 is an elevation of the rotating unit; Fig. l is a detail view of one of the floating contacts, Fig. 5 is a detail view illustrating the unit in the running range; and Fig. 6 is a graph illustrating the operation of the governor.

The invention is herein described as applied to an inverter for converting D. C. to A. 0., although it may be used as a speed control in connection with any electrical machine in which the speed may be varied by a variation in resistance.

The preferred form of the invention comprises two units, namely rotary unit indicated generally at HI and connected with the inverter shaft, and a stationary unit indicated generally at [2 and mounted in fixed position in the frame of the machine.

The rotating unit, asshown in Fig. 3, comprises a stud I4 to be attached to the machine shaft in ill any convenient manner. Preferably the stud I4 is an expansible member which is inserted into a. hole in the end of the inverter shaft, being held in place by an expanding screw l5. Secured to the stud I4 is a frame l8 with resilient side arms 20 arranged to receive the ends of a bowed flat spring 22 to which are riveted the weights 24. A coil spring 26 bears between the base of the frame and the middle of the spring 22. The spring is maintained in centered position surrounding a cylindrical boss 2! on the base of the frame. Wing members 28 for a purpose to be explained later, are attached to the spring 22, preferably by the same rivets which hold the weights 24. The center of the fiat spring is provided with an opening 30.

The stationary unit I2 comprises a cup 32 on which are mounted two metal posts 34 carrying at the outer end a plate 36. As shown in Fig. 1, the posts 34 and plate 36 are held in position by bolts 38, the plate being insulated from the bolts and posts by suitable insulating members indicated at 40. The entire assembly may be enclosed within a cover 4|.

A carbon pile 42, consisting of thin annular disks, is mounted between the cup member 32 and the plate 36. At its ends the pile engages floating contacts 43 and 44 to be later described in detail. An insulating supporting tube 45 for the pile, preferably of glass, passes through the holes in the disks and corresponding holes in the floating supports. The tube is held in place by members 46 and 48.

The member 46 comprises a small plug having inwardly extending spring fingers 50 to engage the inner walls of the tube. As indicated in Fig. 1, the plug is grooved at its under side to accommodate the end of the tube. The plug is received in a central opening 52 in a central boss 53 formed on the plate 35. The peripheral portion of the plug bears against the floating support 44.

The member .8 at the inner end of the tube is similarly provided With spring fingers 54 to engage the inside wall of the glass tube. It will be noted that the fingers 50 and 54 are short enough so that they do not engage one another, and hence the tube forms an insulating support for the carbon pile. Received in the end of the member 43 is a thrust bearing block 56, preferably of Bakelite. in which is received a ball 56, held in place by a suitable retainer 60. The ball 53 is engaged in the opening 30 in the center of the spring 22 of the rotating unit. The member 48 is grooved similarly to the plug 46 to receive the end of the glass tube. The' peripheral portion of the member is adapted to engage the floating contact 43 under some circumstances to be presently described, for which purpose the member 48 is free to pass through a central hole in the cup 32.

The construction of the floating contacts 43 and 44 will now be described. These are of special construction, in order to apply true parallel pressure to all portions of the carbon disks. The contact 43 is a disk having arms 66 extending outwardly at diametrically opposite points and connecting with spring arms 68 which in turn are connected with legs joined with feet 72 bolted under the posts 34. The entire member is made from one integral piece of beryllium copper. The contact member 44 is of identical construction, but the feet 12 are engaged in electrical contact with the plate 36 and insulated from the posts 34. The spring arms 68 act to urge the disks 43 and 44 toward the cup 32 and plate 36, respectively.

The arms 66 and 68 are of spring material, and they may be adjusted with relation to their corresponding contact disks 43, 44 to urge the disks in one direction or the other. For the inner disk 43, the arrangement of the arms is such that the disk is urged into contact with the cup 32. For the outer disk 44, the same setting may be used, in which case the arms tend to force the disk into engagement with the plate 35. Under these conditions the floating members themselves would apply no compression to the pile. Or, as will be explained later, the outer disk 44 may be set with relation to the arms 66, 63 so that the spring pressure of the arms forces the disk away from the plate 36; in other words, if no other forces were acting, the disk 44 would be spaced inwardly from the plate 36 to a slight extent. With such a setting the disk 44 is itself capable of applying some compressive force to the pile. The operation of the apparatus under both conditions will be described later.

The plug member 46 is urged to the left, as viewed in Fig. 5, by a coil spring 14, the compression of which is adjusted by a screw plug 16 threaded into the boss 53. A washer 18 is received within the plug to .bear against the spring. The speed for which the unit is to govern may be adjusted by varying the compression of the spring. A retaining member 80 may be used to prevent accidental removal of the plug.

An electrical lead 82 connects with the plate 36 which forms one terminal of the pile. This lead is connected with the shunt field of the inverter in the usual manner. The other end of the pile is grounded to the frame by reason of the connection of member 43.

..When the device is assembled, as shown in Fig. 1, the springs 22 and 26 of the rotating member are considerably compressed, thereby pressing against the ball 58. At standstill, the force due to these springs overcomes the force of the spring 14, so that the entire carbon pile unit is forced to the right, as shown in Fig. 1. The ball-thrust member 48 bears against the floating member 43, and the member 44 is pressed against the plate 36. The carbon disks are under high compression so that the resistance is a minimum. Consequently, a high field current is available at starting,

As the machine is started, the forces due to rotation of the weights act in a manner to straighten the spring member 22, thus diminishing the spring pressure against the ball 58. The member 48 moves toward the left. At some speed below the running range, the floating contact member 43 bottoms against the cup 32 and the member 48 leaves engagement therewith. At this time, the spring forces due to the rotating member and the spring 14 act only on the tube 45 and are ineffective to apply any compression to the pile. The pile may or may not be then under compression, depending on the setting of the floating contact disk 44 in relation to its arms 66, 58. It has been previously stated that the arms may be adjusted in a manner to urge the disk 44 either toward or away from the plate 36. If the disk is urged toward the plate 36, then at this time the pile will be under no compression and the resistance will be very high, practically infinite. The diminution offield current caused by the presence of this high resistance in the field circuit accelerates the speed-up of the machine. It will be noted that the space taken by the pile and floating members is slightly less than the space between the cup 32 and the plate 36, which constitute the end supports for the pile, whereby a small lost motion is provided. The setting of the disk 44 to provide a substantially infinite resistance is satisfactory in machines having a light series field, thus assuring rapid acceleration in the intermediate range.

For larger units, it may be necessary to maintain some shunt field current in order that the torque will not be too greatly reduced. To this end the disk 44 is set to be urged by its spring arms 66, 68 away from the plate 36, that is, toward the pile, so that it applies some c0m pression to the pile even when the other springs apply no compression thereto. The compression thus applied to the pile by the disk 44, in this intermediate range is less than that applied by the other springs of the unit in the starting or running range. The amount of compression, and hence the maximum resistance in the intermediate range, may obviously be adjusted by the pressure applied by the floating contact disk 44.

In any case, as the speed further increases the force due to the rotating member further diminishes. Under the action of spring 14 the plu 46 then engages the floating disk 44, as shownin Fig. 5, and the pile is again subjected to strong compression between the floating member 44 and the now stationary member 43. The control is now in the running range, wherein the disks are variably compressed in dependence on speed. If the speed increases above the regulated value, the disks are compressed further to increase the field current, and if speed is reduced, the compression is relaxed to decrease the field current, whereby the inverter speed is quickly restored to the desired value.

It will be seen that in the starting range the pile is compressed toward the right and in the running range it is compressed toward the left, while the lost motion provides an intermediate condition of zero (or minimum) compression to accelerate the speeding up of the machine. Between starting and running conditions, th pile is shifted bodily from one position (Fig. 1) to the other (Fig. 5).

A graph illustrating typical operation is given in-Fig. 6. This is for an inverter having a rated speed of 8000 R. P. M. At standstill the resistance of the pile is 0.20 ohm. At 4500 R. P. M. the resistance has increased to 0.50 ohm. Above 4500 R. P. M. the resistance increases rapidly.

If zero compression is applied in the intermediate range, the resistance rises toward infinity, as indicated by the solid line. If some compression is maintained in the intermediate range, the intermediate range is as illustrated generally by the dotted portion of the curve. The running range is indicated as beginning at about 7980. At the desired speed of 8000, the resistance may be about 20 ohms; the curve is there very steep, so that a sensitive control of speed is readily obtained.

The regulated speed may be adjusted by varying the compression of the spring 14, which is easily accomplished by adjusting the screw 16.

The construction of the rotating unit is of importance. The spring forces of the rotary unit are made up of the forces due to the resilient arms 20 of the frame, the flexure of the flat spring 22 and the force due to the coil spring 26. The coil spring is desirable because the large force required for compression of the pile could not be provided by a flat spring of convenient size. The wing members 28 are used to flex the flat spring 22 and compress the coil spring 26; they prevent any tendency of the flat spring to buckle.

The rotary unit is preferably so adjusted that at the regulated speed, the spring 22 is nearly straight but slightly bowed outwardly as shown in Fig. 5. In this position the forces due to the arms 20 and the flat spring 22 are relatively weak as compared with the corresponding forces under the starting condition (Fig. 1) when the spring 22 is bowed outwardly to a greater extent. Thus in the running range, a soft and sensitive spring action is provided.

This application is a division of my application No. 587,103, filed April 7, 1945.

Having thus described the invention, I claim:

1. A resistance apparatus including a pile of pressure responsive resistance elements, a pair of rigid abutments, for said pile separated by a distance slightly greater than the length of the pile, floating contact members for said pile, one

of said floating contact members being disposed immediately adjacent one of said rigid abutments and the second of said floating contact members being disposed immediately adjacent the second of said rigid abutments, pressure applying means acting upon the first-named floating contact, and a second pressure applying means acting upon the second-named floating contact and opposing said first pressure applying means and acting in a direction to compress the pile directly against the second-named rigid abutment and thereby eliminate the eifect of one of said floating contact members, so long as said pile remains compressed against the adjacent rigid abutment.

2-. A resistance apparatus including a pile of pressure responsive resistance elements, rigid supports for said pile separated by a distance slightly greater than the length of the pile, floating contact members for said pile, one of said floating contact members being disposed immediately adjacent one of said rigid supports and the second of said floating contact members being disposed immediately adjacent the second of said rigid supports, pressure applying means acting upon the first-named floating contact, a second pressure applying means opposing said first pressure applying means and acting in a direction to compress the pile against the second-named support, and means engaging the second-named floating contact member to compress the pile during one portion of the cycle of operation, said means being disengaged during another portion of the cycle.

3. In a carbon resistance mechanism, a stack of carbon elements, a rigid abutment adjacent one end of said stack, a rigid abutment adjacent the opposite end, a floating abutment interposed between said stack and one of said rigid abutments, means urging said floating abutment away from said rigid abutment to apply pressure to one end of said stack, and means for overcoming said urging means and thereby causing said stack to press directly against the abutment nearest to said urging means and thus remove the influence of said floating abutment upon said stack.

4. In a carbon resistance mechanism, a stack of carbon elements, a floating abutment adjacent one end of said stack, a rigid abutment adjacent said floating abutment, resilient means acting upon said floating abutment to apply pressure to said one end of said stack, and means including a second resilient means for overcoming said first-named resilient means, said second resilient means operating to press said stack against said rigid abutment adjacent said floating abutment, said overcoming means operating to press said stack against said rigid abutment when the infiuence of said floating abutment has been removed.

5. In a carbon resistance mechanism, a stack of carbon elements, a rigid abutment adjacent one end of said stack, a rigid abutment adjacent the opposite end, means for compressing said stack in one direction, against one'of said abutments, during one stage in a complete cycle of operation, and means for oppositely compressing said stack, against the opposite abutment, during a different stage in said cycle.

FRED P. VACHA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,681,314 Vawter Aug. 21, 1928 1,939,870 Wike Dec. 19, 1933 2,339,749 Albers Jan. 25, 1944 2,393,951 Austin Feb. 5, 1946 2,406,449 Whittaker Aug. 27, 1946 2,454,671 Roberts Nov. 23, 1948 2,460,246 Vacha Jan. 25, 1949 FOREIGN PATENTS Number Country Date 471,422 Great Britain Sept. 3, 1937 

